Answer:
There are 81 numbers
Step-by-step explanation:
Imagine that you have 4 boxes (one for each digit). In each box, you only have 3 choices for what digit you will do. You have to multiply all of the options (3*3*3*3) and you get 81.
308
21
It is 21 since 21 = 3 * 7.
The other 3 numbers are prime.
45x to the 3rd power y divided by 9xy
5x to the 3rd power y
